A wind turbine known in the art comprises a wind turbine tower and a wind turbine nacelle positioned on top of the tower. A wind turbine rotor with a number of wind turbine blades is connected to the nacelle through a low speed shaft, which extends out of the nacelle front as illustrated on FIG. 1.
The demands to large modern wind turbines are constantly increasing—especially regarding output. And the bigger output the wind turbine has to produce, the bigger the entire wind turbine and the different parts of the wind turbine has to be. But large modern wind turbines are already so large that it is an increasing problem to transport and erect them. It is therefore essential that the different parts of the wind turbine are made to be as efficient as possible to produce more energy without increasing the size.
Especially regarding wind turbine blades, this development has been profound. To increase the output, the blades are designed as optimal as possible regarding energy conversion of the wind and the blades are used more efficiently regarding angle of attack to the incoming wind. But the downside of this is that the blades more easily stall, or at least that the blades stall over a larger area of the blade.
One of the major consequences of stall is noise emission, and stall induced noise from the blades are almost always the main source of noise from modern wind turbines. This problem can be dealt with in different ways and one of them is disclosed in international patent WO 01/16482 where the blades of a relatively small stall controlled wind turbine are provided with vortex generators. The vortex generators create turbulence in the passing air, hereby reducing the area of the blade where stall occurs or completely eliminating stall. But wind turbines, and thereby also the wind turbine blades, are typically made to last 20 years, and in that these vortex generators are highly exposed to UV radiation, rain, snow, hail and great variations in temperatures besides being constantly drawn through the air at very high speed, the risk of the vortex generators being torn from the blade surface is very high. The vortex generators could of course just be repaired or replaced, for example, in certain intervals, but the blades are not easy to access and the downtime of large modern wind turbines are very costly.
An object of the invention is therefore to present an advantageous technique for providing a wind turbine blade with turbulence generating means.
Especially, it is an object to provide for a technique which ensures that the turbulence generating means maintains their desired function for a long time.
Furthermore, it is an object of the invention to provide for an advantageous technique for providing a wind turbine blade of a pitch controlled wind turbine with turbulence generating means.